NCERT Class VII Science Solutions: Chapter 18-Wastewater Story Part 3

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SHORT ANSWER QUESTIONS

Question 14:

Name two inorganic impurities present in sewage.

Answer:

Nitrates, Phosphates, Metals (any two).

Question 15:

Animal waste, oil and urea are some of the organic impurities present in sewage. Name two more organic impurities present in sewage.

Answer:

Pesticides, herbicides, fruits and vegetable waste (any two).

Question 16:

Name two alternative arrangements for sewage disposal where there is no sewerage system.

Answer:

  1. Septic tanks

    Image of Septic tank

    Septic Tank

    Image of Septic tank

  2. Composting pits

Question 17:

A man travelling in a train threw an empty packet of food on the platform. Do you think this is a proper waste disposal method? Elaborate.

Answer:

No, one must always put the waste in a nearby dustbin or carry it until a proper place to dispose it of is found. Waste, not properly disposed may go into the drains and choke them. It also makes public places dirty and unhygienic.

Question 18:

Why should we not throw?

  1. Used tea leaves into sink?

  2. Cooking oil and fats down the drain?

Answer:

  1. Used tea leaves may choke the drain-pipe of the sink.

  2. Cooking oil and fats can harden and block the pipes.

Question 19:

Match the items of Column I with the Items of Column II with reference to sewage.

Match the Column I and Column II (Q)
Match the Column I and Column II (Q)

Column I

Column II

Inorganic impurities

Phosphorus and nitrogen

Organic impurities

Nitrates and phosphates

nutrients

Cholera and typhoid

Bacteria

Pesticides and herbicides

Answer:

Match the Column I and Column II (A)
Match the Column I and Column II (A)

Column I

Column II

Inorganic impurities

ii Nitrates and phosphates

Organic impurities

iv Pesticides and herbicides

nutrients

i Phosphorus and nitrogen

Bacteria

iii Cholera and typhoid

Question 20:

Given below is a jumbled sequence of the processes involved in a wastewater treatment plant. Arrange them in their correct sequence.

  1. Sludge is scraped out and skimmer removes the floating grease.

  2. Water is made to settle in a large tank with a slope in the middle.

  3. Large objects like plastic bags are removed by passing wastewater through bar screens.

  4. Sand, grit and pebbles are made to settle by decreasing the speed of incoming wastewater.

  5. Wastewater enters a grit and sand removal tank.

Answer: